Defect Summary:
VEHICLE DESCRIPTION: HEAVY DUTY TRUCKS EQUIPPED WITH OPTIONAL WABCO AIR DRYER. THE AIR BRAKE SYSTEM WAS PLUMBED SO THAT THE SYSTEMS DID NOT PROVIDE AIR RESERVOIR ISOLATION. THIS DOES NOT COMPLY WITH THE REQUIREMENTS OF FMVSS NO. 121, “AIR BRAKE SYSTEMS.”

Consequence Summary:
THE AIR BRAKE RESERVOIR PRESSURE COULD BE DEPLETED, ACTIVATING THE EMERGENCY SPRING BRAKE. WITH THE EMERGENCY SPRING BRAKE DEPLOYED, THE VEHICLE WOULD STOP AND COULD NOT BE MOVED UNTIL THE BRAKE AIR SYSTEM WAS REPAIRED.

Corrective Action:
DEALERS WILL REPAIR THE AIR LINE PLUMBING TO INSTALL A CHECK VALVE.